A conventional filter assembly for filtering-out contaminants from a lubricating or working fluid normally comprises a stationary housing having an annular cartridge-type filter removably mounted therein. A bypass valve of the poppet-type is normally mounted in the filter assembly to open and communicate fluid from the inlet to the outlet thereof directly, when the filter becomes clogged, for example. Filter assemblies of this type are exemplified by U.S. Pat. Nos. 2,886,180; 3,556,300; and 3,628,661 and U.S. application Ser. No. 562,383 filed on Mar. 26, 1975 by A. L. Kufuss for "Removable Filter Assembly With Bypass Valve", all assigned to the assignee of this application.
One disadvantage of such filter assemblies is their inability to modulate fluid pressure in the system upon opening of the bypass valve. In addition, the poppet valves thereof are highly sensitive to pressure pulsations and thus function as a "shock absorber" to open even during normal filtering operations. An opening of only one-sixteenth of an inch, for example, will bypass unfiltered oil through the system.